Mr Red, your site looks fine to me (thought I don't know what I may be missing), and the advert popped up but then vanished, which I suspect is as good as you're going to get if you've put in code to kill the advert.

Sadly the lowest common denominator is technically fairly low
One of the problems especially with Javascript is that there are many different versions, supported to different degrees by different browsers. HTML and CSS are moving targets too. Most browsers have pretty good CSS1 compliance by now, and can display PNG which is the royalty-free alternative to GIF.

But a page does not have to leave out everything that isn't supported by all browsers. The idea is that if a browser doesn't have some capability, the site will degrade gracefully and all the content will still be available.

So for example a fancy Java based navigation system is fine, as long as it's backed up by usable plain HTML navigation system which
reaches all the same information.

Anahata